Method for manufacturing an opening structure and opening structure

ABSTRACT

A method for manufacturing an opening structure is provided. The method may include: forming a patterned mask over a first side of a carrier; forming material over the first side of the carrier covering at least a portion of the carrier; forming a first opening in the carrier from a second side of the carrier opposite the first side of the carrier to at least partially expose a surface of the patterned mask; and forming a second opening in the material from the second side of the carrier using the patterned mask as a mask.

RELATED APPLICATION(S)

This application is divisional of U.S. patent application Ser. No.14/285,839, filed May 23, 2014, and entitled “METHOD FOR MANUFACTURINGAN OPENING STRUCTURE AND OPENING STRUCTURE”, the contents of which areincorporated herein by reference in their entirety.

TECHNICAL FIELD

Various embodiments relate generally to a method for manufacturing anopening structure and to an opening structure.

BACKGROUND

During manufacture of microelectromechanical systems (MEMS) or othersemiconductor elements, an etching of deep openings, trenches orcavities from a back side of a substrate/carrier extending to a frontside of the substrate may often be required.

For a good functionality of the final element, it may be essential thata relative positioning (adjustment) of a backside mask with respect tostructures on the front side of the substrate is precise. Furthermore,the positioning of structures defined by the mask on the back side ofthe substrate may need to be transferred precisely to the front side ofthe substrate, and a shape of the structures defined on the back sidemay need to be conserved during the transfer from the back side to thefront side of the substrate, such that openings/trenches/cavities havingbeen formed in the substrate from the backside and opening up on thefront side of the substrate are precisely positioned with respect to thefront side structures and have an intended shape.

Such aspects may for example be relevant in the manufacturing of siliconmicrophones or loudspeakers.

SUMMARY

A method for forming an opening structure is provided. The method mayinclude: forming a patterned mask over a first side of a carrier;forming material over the first side of the carrier covering at least aportion of the carrier; forming a first opening in the carrier from asecond side of the carrier opposite the first side of the carrier to atleast partially expose a surface of the patterned mask; and forming asecond opening in the material from the second side of the carrier usingthe patterned mask as a mask.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. The drawings are not necessarilyto scale, emphasis instead generally being placed upon illustrating theprinciples of the invention. In the following description, variousembodiments of the invention are described with reference to thefollowing drawings, in which:

FIG. 1A to FIG. 1D show cross sections of devices with misalignedopening structures;

FIG. 2A and FIG. 2B show bottom views of faulty openings;

FIG. 3A and FIG. 3B show cross sections of devices with misalignedopening structures;

FIG. 4A to FIG. 4D show a process flow for a method for forming anopening structure in accordance with various embodiments;

FIG. 5A to FIG. 5H show a process flow for a method for forming anopening structure in accordance with various embodiments;

FIG. 6A and FIG. 6B show cross sections of opening structures accordingto various embodiments;

FIG. 7A to FIG. 7E show a process flow for a method for forming anopening structure in accordance with various embodiments;

FIG. 8A and FIG. 8B show cross sections of opening structures accordingto various embodiments;

FIG. 9 shows a schematic diagram of a method for forming an openingstructure in accordance with various embodiments;

FIG. 10A to FIG. 10D show a process flow for a method for forming anopening structure in accordance with various embodiments;

FIG. 11A to FIG. 11C show a process flow for a method for forming anopening structure in accordance with various embodiments; and

FIG. 12 shows a schematic diagram of a method for forming an openingstructure in accordance with various embodiments.

DESCRIPTION

The following detailed description refers to the accompanying drawingsthat show, by way of illustration, specific details and embodiments inwhich the invention may be practiced.

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration”. Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs.

The word “over” used with regards to a deposited material formed “over”a side or surface, may be used herein to mean that the depositedmaterial may be formed “directly on”, e.g. in direct contact with, theimplied side or surface. The word “over” used with regards to adeposited material formed “over” a side or surface, may be used hereinto mean that the deposited material may be formed “indirectly on” theimplied side or surface with one or more additional layers beingarranged between the implied side or surface and the deposited material.

FIG. 1A to FIG. 1D show opening structures in devices 100. Each of thefigures shows: a substrate 102, a mask 108 arranged below the substrate102 on a back side of the substrate 102, a top layer 104, for example asilicon oxide layer 104, arranged over the substrate 102 on a front sideof the substrate 102 opposite the back side of the substrate 102, astructure 106 arranged over the top layer 104 on the front side of thesubstrate 102, and an opening 110 extending through the substrate 102from the back side of the substrate 102 to the front side of thesubstrate 102.

Relative positioning of the back side mask 108 with respect to the frontside structure 106, using tools presently available, may reach only alow precision of about 5 μm. This is shown in FIG. 1A, where the opening110 in the substrate 102 is misplaced laterally (parallel to the frontside and the back side, respectively), such that the structure 106 andthe opening 110 are misaligned. An optimal relative positioning of theopening 110 and the front side structure 106 is shown as dashed lines109.

In various embodiments, the substrate 102 may have a thickness of about300 μm or more, in various other embodiments the thickness of thesubstrate 102 may be below 300 μm. The opening 110 may extend from theback side of the substrate 102 to the front side of the substrate 102(thereby exposing a portion of a surface of the top layer 104. It may beetched using plasma etching, for example using a Bosch deep reactive ionetching process. The etching process etching such a large depth maycause the etched structure (e.g. the opening 110) to be tilted. In otherwords, whereas one end of the opening 110 close to the mask 108 may bevery well aligned with the mask 108, another end of the opening 110,which is further away from the mask 108 by a distance y in a directionindicated by an arrow in FIG. 1B, may be laterally offset. The offsetmay for example be linear towards one lateral direction with increasingdistance y from the mask 108. Such an offset may also be referred to astilting. The tilting may cause an offset of structures defined by themask 108 with respect to the front side structure 106. The magnitude andthe direction of the tilting may depend on a state of an etching chamberand may not be stable.

As shown in FIG. 1C and FIG. 1D, etching of the opening 110 by means ofplasma etching may cause a narrowing (FIG. 1C) or a broadening (FIG. 1D)of the opening 110 in the direction y in FIG. 1C and FIG. 1D, generallya change in size. In other words, near the front side of the substrate102, the opening 110 may be narrower or broader than defined by the mask108 on the back side of the substrate 102. This may cause a misalignmentof the structures defined by the mask 108 with respect to the front sidestructure 106. The magnitude and the direction of thenarrowing/broadening may depend on a state of an etching chamber and maynot be stable.

FIG. 2A shows a view of the device 100 as seen from the bottom in one ofFIG. 1A to FIG. 1D. It shows that spontaneous polymerization during theetching of the opening 110 may cause a roughening of walls of theopening 110. This may cause a rough and/or irregular end 214 of theopening 110 on the front side of the substrate 102, despite a smoothstructure 212 defined by the mask 108 on the back side of the substrate102. The magnitude of the roughening may depend on a state of an etchingchamber and may not be stable.

Alternatively, wet-chemical etching may be used for etching the opening110 in the device 100 according to FIG. 1A. Even though wet-chemicaletching may be cheap, large variations between sizes of the structuresdefined on the back side of the substrate 102 by the mask 108 andstructures obtained on the front side of the substrate 102 by thewet-chemical etching may be caused. Furthermore, a change in shape ofthe structures defined on the back side of the substrate 102 by the mask108 and structures obtained on the front side of the substrate 102 bythe wet-chemical etching may occur due to an etching rate that dependson a crystallographic structure and orientation of the substrate 102.This is shown in FIG. 2B, where the round structure 212 is defined bythe mask 108 on the back side of the substrate 102, and a quadraticstructure with rounded corners 216 is obtained on the front side of thesubstrate 102. This change in shape may be so severe as to beprohibitive to using wet-chemical etching for forming the openings 110in silicon microphones or (e.g. micro) loudspeakers.

FIG. 3A and FIG. 3B show two possible effects of misaligned structuresformed by the mask 108 on the back side of the substrate 102 andincorrectly transferred by means of etching to the front side of thesubstrate 102, as described for the examples in FIG. 1A to FIG. 1D. InFIG. 3A and FIG. 3B, the device may be a silicon microphone (some partslike a gap, counter electrode and the like are not shown), with thefront side structure 106 including or being a membrane. The opening 110may be etched, for example by etching of the substrate 102, using forexample plasma etching, for example Bosch etching, and/or wet etching,and of the top layer 104, for example using wet-chemical etching usinghydrogen fluoride and/or using plasma etching. The shape of the opening110 in the substrate 102, i.e. its edge on the front side of thesubstrate 102, may define a shape of the top layer 104 (i.e. the layerof silicon oxide 104 as described above, for example), for example asilicon oxide layer, which serves as support for the membrane 106. In acase like it is shown in FIG. 3A, a widening of the opening 110 from theback side towards the front side of the silicon microphone 100 may causethe top layer 104 (the supporting oxide layer 104) to be etched up to apoint where the top layer 104 is not in contact with the membrane 106anymore (see e.g. faulty region 318 in FIG. 3A) and thus cannot supportthe membrane 106. Such a lack of support of the membrane 106 means thatthe silicon microphone will become defective. As shown in FIG. 3B, themisaligned structures (in this case a lateral offset) may also lead to asituation where the substrate 102, for example a silicon substrate, isnot etched away in a region opposite a vent hole in the membrane 106(see e.g. faulty region 318 in FIG. 3B). An edge of the substrate 102covering the vent hole may cause a wrong acoustic frequency response.

Furthermore, the rough end 214 of the opening 110 on the front side ofthe substrate 102, as shown in FIG. 2A, may lead to a decrease inrobustness of the device 100, for example the silicon microphone.

In a device, one or more of the above described problems may be presentat the same time.

At present, satisfactory means to overcome the problems described abovemay not exist. Complex measurements checking the alignment of the backside mask 108 with respect to the front side may be conducted, andwafers outside specifications may be re-worked. This may causeadditional production overhead. Furthermore, with the wafer, for examplean 8″ wafer, typically having been thinned to its final thicknessalready, an extra handling may increase a risk of wafer damage.

In order to adjust for a change in size and/or tilting of the openings110 defined by the structured mask 108, measurements may be conductedand analyzed statistically. Results may be used to structure the mask108 in a way which, on average, may lead to the desired positioning ofthe structure on the front side of the substrate 102. In other words, inorder to make the structure end up in the desired location on the frontside of the substrate 102, despite an offset expected from statisticalevaluation of measurements on a batch of devices of a production line,the mask 108 is shifted opposite the expected shift by the expectedamount. Similarly, a widening/narrowing of the structure on the frontside of the substrate 102 with respect to the back side of the substrate102, determined from a statistical analysis of measured structure sizeson the back side of the substrate 102 and the front side of thesubstrate 102, may be attempted to be employed for leading to thedesired structure on the front side of the substrate 102 bynarrowing/widening the structure of the mask 108 by a correspondingamount/factor.

The statistical nature of the above described errors, the appliedcorrections and further production uncertainties may lead to faultysystems despite the applied corrections. For a detection of faultysystems, measurements may be necessary that require dedicatedmeasurement systems and the measuring of all wafers of a given lot of aplurality of wafers.

The roughness of the end 214 of the opening 110 on the front side of thesubstrate 102 may be smoothed to some extent, but not completely avoidedby the plasma opening etching process, because spontaneouspassivation/polymerization may not be controlled. An etching processreducing spontaneous passivation may have to be less selective withrespect to a material of the mask 108. However, further reducingselectivity of the presently used mask material (e.g. photoresist) maynot be possible. Furthermore, an etching process designed to reduce theroughness of end 214 of the opening 110 may additionally be slower,which may require additional production capacity for opening etching(for example using a Bosch etching process).

The above described problems may be solved by forming a hard patternedmask within a substrate near a surface of a front side of the substrate102.

FIG. 4A to FIG. 4D show a process flow for a method for forming anopening structure in accordance with various embodiments.

As shown in FIG. 4A, the method for manufacturing an opening structure400 may, in various embodiments, include forming a patterned mask 424over a first side 426 of a carrier 420.

The carrier 420 may for example include or consist of silicon or anothersemiconductor material. An etch selectivity (i.e. a ratio of an etchingrate of a first material and of an etching rate of a second material)may for example be in the range from about 50 to about 2000,meaning thatthe etching rate of the carrier 420 material may be about 50 to about2000 times as high as the etching rate of the mask 424 material.

In various embodiments, the carrier 420 may have a thickness b, whereinthe thickness b may be a distance between the first side 427 of thecarrier and the second side 426 of the carrier 420. The thickness b ofthe carrier 420 may be in a range from about 50 μm to about 600 μm, e.g.from about 300 μm to about 500 μm, e.g. about 300 μm or about 400 μm.

In various embodiments, the patterned mask 424 may have a first surface423, wherein the first surface 423 of the patterned mask 424 may befacing towards the carrier 420, another surface (also referred to assecond surface) 425 opposite the first surface 423, an inner rim 419 andan outer rim 421. The material of the patterned mask 424 may include orbe any material that has a high etch selectivity with respect to thecarrier 420 material. The patterned mask 424 may be a hard mask. Thepatterned mask 424 may for example be formed by forming the mask 424 asa continuous layer over the first side 426 of the carrier 420, and thenstructuring it photolithographically. The patterned mask 424 may have athickness in the range from about 5 nm to about 1 μm, for example fromabout 300 nm to about 800 nm, for example from about 500 nm to about 700nm. In various embodiments, the thickness of the patterned mask 424 maydepend on a ratio of the etching rate of the material of the patternedmask 424 with respect to the etching rate of the carrier 420 material.If the etching rate of the carrier 420 is much higher than the etchingrate of the patterned mask, for example 1000 times as high, thepatterned mask 424 may have a thickness in the range from about 5 nm toabout 50 nm. If the ratio of etching rates, i.e. the etch selectivity,is not as high, for example 100, i.e. the etching rate of the carrier420 material is about 100 times as high as the etching rate of thepatterned mask 424, the thickness of the patterned mask may be in therange from about 200 nm to about 1000 nm. In various embodiments, thethickness of the patterned mask may depend on subsequent processes, forexample an initial thickness of the patterned mask 424, for example 850nm, may be larger than a final thickness of the patterned mask 424 inorder to account for chemical mechanical polishing/planarization (CMP)of the patterned mask 424. In various embodiments, subsequent processesmay involve heating of the opening structure. Hence, the mask 424material may be temperature resistant. In various embodiments, the mask424 material may include or consist of at least one material from thefollowing group of materials, the group including or consisting of anoxide, e.g. silicon dioxide, aluminum oxide or silicon oxynitride, anitride, e.g. silicon nitride, carbon, a carbon compound, e.g. diamondlike carbon, a carbide, e.g. silicon carbide, and high temperatureresistant metals, e.g. tungsten.

In various embodiments, a first mask portion 424 a and a second maskportion 424 b of the mask 424 may join in front of and behind a planeshown in the cross section, such that they may form a closed structure,like a ring or a rectangular frame or a connected structure with oneopening. In various other embodiments, the two portions of the mask 424a and 424 b may be separated from each other. In various embodiments, anarbitrary number of mask portions which may be separated from eachothermay be provided.

In various embodiments, the method may further include forming material422 over the first side 426 of the carrier 420 covering at least aportion of the carrier 420. The material 422 may further cover at leasta portion of the patterned mask 424. A buried patterned mask 424 maythus be formed. In various embodiments, the material 422 may include orconsist of a material with an etching rate that is substantially higherthan that of the mask 424. The etching rate of the material 422 may forexample be about 50 to about 2000 times as high as the etching rate ofthe mask 424. In various embodiments, the material 422 may be or includethe same material as the carrier 420. The material 422 may for examplebe or include silicon, for example amorphous silicon, or for examplepolycristal silicon (also referred to as polysilicon). In variousembodiments, the material 422 may include some other material of a typesimilar to the material of the carrier 420, for example with respect toremoval characteristics, e.g. etching characteristics during a plasma-or wet chemical etching, and/or electrical or mechanical properties. Thematerial 422 may for example be another semiconductor material. Invarious embodiments, the material 422 may be doped. The doping may beperformed in situ, i.e. during the forming of the material 422. In thisway, subsequent high-temperature processes may be avoided, and a goodelectrical connectivity to the carrier 420 may be achieved.

In various embodiments, the material 422 may be formed in a singleforming process. In various other embodiments, the material 422 may beformed in two or more individual forming processes, wherein otherprocesses, such as etching or polishing, may be executed between the twoor more individual forming processes.

In various embodiments, the material 422 may have a first thickness a,wherein the first thickness a may be a distance between a first surfaceof the material 422 facing the first side 426 of the carrier 420 and asecond surface of the material 422 opposite the first surface of thematerial 422. The first thickness a of the material 422 may be in arange from about 500 nm to about 5 μm, for example from about 800 nm toabout 1.2 μm, for example around 1.1 μm or for example around 2 μm.

In various embodiments, the material 422 may have a second thickness cabove the patterned mask 424. The second thickness c may be a distancebetween the second surface 425 of the patterned mask 424 and the secondsurface of the material 422. In various embodiments, the secondthickness c of the material 422 may be smaller than the first thicknessa of the material 422. In various embodiments, the first thickness a andthe second thickness c of the material may be the same. In variousembodiments, the second thickness c of the material 422 may be below 3μm, for example between 1 μm and 2 μm. In various embodiments, thesecond thickness c of the material 422 may be zero.

The material 422 may be formed over the first side 426 of the carrier420 by means of deposition, for example by means of plasma deposition,chemical vapor deposition (CVD) or selective epitaxial growth (SEG).

In various embodiments, a surface of the material 422 opposite thecarrier 420 may be smoothed, for example by means of chemical mechanicalpolishing/planarization.

As shown in FIG. 4B, in various embodiments, the method formanufacturing the opening structure 400 may further include forming afront side structure 429 over the material 422. In various embodiments,the front side structure 429 may include any kind of structure formedover the material 422 that requires an accurate positioning over a firstside 426 of the carrier 420 (on the front side of the carrier 420) withrespect to an opening to be formed from a second side 427 of the carrier420 (from the back side). The front side structure 429 may for exampleinclude a microelectromechanical component or structure, a mechanicalcomponent or structure and/or an electronic component or structure. Invarious embodiments, the front side structure 429 may include or consistof two layers 428 and 430, or more than two layers. In various otherembodiments, the front side structure 429 may only include or consist ofone of the two layers 428 and 430. For example, the front side structure429 may be formed as a single layer, or it may be formed by a pluralityof layers, and some of the layers may be partially or completely removedlater, for example after having served as protection or support.

The forming of the front side structure 429 may, in various embodiments,include forming a first layer 428 over the material 422. In variousembodiments, the first layer 428 may be a continuous layer.Alternatively, the first layer 428 may be a discontinuous layer. Thefirst layer 428 may for example be structured. In various embodiments,the first layer 428 may be a single layer. Alternatively, the firstlayer 428 may include or consist of a plurality of layers. In variousembodiments, the first layer 428 may consist of or include a singlematerial. Alternatively, the first layer 428 may consist of or includemore than one material. The first layer 428 may for example include orconsist of at least one material from a group of materials, the groupincluding or consisting of an oxide, for example silicon dioxide,silicon oxynitride, and a glass, for example borophosphosilicate glass.The first layer 428 may have a thickness in a range from about 100 nm toabout 1 μm, for example from about 300 nm to about 500 nm. The firstlayer 428 may for example be deposited, for example by means of plasmadeposition or chemical vapor deposition (CVD).

As further shown in FIG. 4B, the method may include forming a secondlayer 430 over the first layer 428. In various embodiments, the secondlayer 430 may be a discontinous layer. Alternatively, the second layer430 may be a continuous layer. The second layer 430 may for example bestructured. It may for example be a discontinuous or continuousstructured layer. The second layer 430 may for example be deposited, forexample by means of plasma deposition or chemical vapor deposition(CVD), for example thermal CVD. In various embodiments, the second layer430 may be a single layer. Alternatively, the second layer 430 mayinclude a plurality of layers. In various embodiments, the second layer430 may consist of or include a single material. Alternatively, thesecond layer 430 may include more than one material. The second layer430 may for example include or consist of at least one material from agroup of materials, the group including or consisting of asemiconductor, for example silicon, for example polysilicon, and anoxide, for example silicon dioxide.

In various embodiments, at least one of the first layer 428 and thesecond layer 430 may be positioned precisely with respect to thepatterned mask 424. In other words, in particular when the first layer428 and/or the second layer 430 is structured and/or does not cover thesurface on which it is formed, the first layer 428 and/or the secondlayer 430 may be arranged, within a plane of the respective layer 428and/or 430, in such a way that the structures and/or circumference ofthe layer 428 and/or 430 are located in pre-defined relative positionswith respect to the patterned mask 424.

As shown in FIG. 4C, in various embodiments, the method may furtherinclude forming a first opening 532 in the carrier 420 from the secondside 427 of the carrier 420 opposite the first side 426 of the carrier420 to at least partially expose a surface 423 of the patterned mask424.

In various embodiments, the first opening 532 may be a cavity. Invarious embodiments, the first opening 532 may be a trench. The firstopening 532 may be etched, for example by means of plasma etching or/andwet chemical etching. A region to be etched may be defined by means of asecond mask 533, for example a structured second mask 533. The secondmask 533 may be formed on the second side 427 of the carrier 420. Thesecond mask 533 may have a first side facing the second side 427 of thecarrier 420, and a second side opposite the first side of the secondmask 533.

The second mask 533 may include or consist of a material with a highetch selectivity with respect to the carrier 420. The patterned secondmask 533 may for example be formed by forming the second mask 533 as alayer over the second side 427 of the carrier 420, and then structuringit photolithographically. In various embodiments, the second mask 424material may include or consist of at least one material from thefollowing group of materials, the group including or consisting of anoxide, e.g. silicon dioxide, aluminum oxide or silicon oxynitride, anitride, e.g. silicon nitride, carbon, a carbon compound, e.g. diamondlike carbon, a carbide, for example silicon carbide, and hightemperature resistant metals, e.g. tungsten.

In various embodiments, the first opening 532 may extend from the secondside of the second mask 533 through the second mask 533 and the carrier420 to the first side 426 of the carrier 420. In this case, a depth ofthe first opening 532 may be a sum of the thickness b of the carrier 420and the second mask 533. In other embodiments, for example after aremoval of the second mask 533, the first opening 532 may extend fromthe second side 427 of the carrier 420 through the carrier 420 to thefirst side 426 of the carrier 420, i.e. a depth of the first opening 532may be the thickness b of the carrier 420. The first opening 532 mayalso be described as extending between a first end of the first opening532 near the first side 426 of the carrier 420 to a second end of thefirst opening 532 near the second side 427 of the carrier 420(irrespective of whether the second mask 533 is still on the carrier 420or not).

In various embodiments, the first opening 532 may be arranged on/in thecarrier 420 in such a way that it at least partially exposes a surface423 of the patterned mask 424. In other words, the first opening 532 maybe arranged in the carrier 420 such that virtual planes coinciding withside walls 535 of the first opening 532 and extending beyond the sidewalls 535 towards the patterned mask 424 cut through the patterned mask424. In various embodiments, said virtual planes may cut through thepatterned mask 424 along an entire circumference formed by the sidewalls 535 of the first opening 532. Phrasing it in a yet different way,the forming of the first opening 532, for example the etching of thefirst opening 532, from the second side 427 of the carrier 420 may stop,at least near the circumference of the first opening 532, on thepatterned mask 424. In various embodiments where the mask 424 is formedby the first mask portion 424 a and the second mask portion 424 b, orwhere the mask 424 may not form a closed circumference, but acircumference with one opening, said virtual planes may cut through thepatterned mask 424 only in regions where the patterned mask 424 ispresent. In various embodiments, said virtual planes may not cut throughthe material 422 without cutting through the mask 424 first. By formingthe first opening 532 according to any of the described embodiments, asurface 423 of the patterned mask 424 may be at least partially exposed.In various embodiments, a size of the first opening parallel to thefirst side 426 may not be larger than a size of the mask 424, i.e. adistance between opposing points on the outer rim 421 of the patternedmask 424.

In that case, the first opening 532 may be formed into the carrier 420such that at least a portion of a first mask portion 424 a of thepatterned mask 424 and at least a portion of a second mask portion 424 bof the patterned mask 424 are exposed by the first opening.

In various embodiments, as shown in FIG. 4D, the method may furtherinclude forming a second opening 536 in the material 422 from the secondside 427 of the carrier 420, using the patterned mask 424 as a mask.

In various embodiments, the second opening 536 may be a cavity. Invarious embodiments, the second opening 536 may be a trench. Forexample, in various embodiments, the second opening 536 may extend fromthe first side 426 of the carrier 420 through the material 422 to thesecond surface of the material 422, i.e. a depth of the second opening536 may be the thickness a of the material 422. In various embodiments,the first opening 532 may be formed with a larger width than the secondopening 536, i.e. a distance between opposite points on an edge 535 ofthe carrier 520 along the first opening 532 may be larger than adistance between opposite points on an inner rim 537 of the material422, measured in the same direction.

In various embodiments, the second opening 536 may be etched, forexample by means of plasma etching, for example a Bosch etching process,or/and wet chemical etching. In various embodiments, the second opening536 may for example be etched anisotropically, e.g. by means of a Boschetching process. This may lead to the second opening 536 with an innerrim 537 of the material 422 that is flush with an inner rim 419 of thepatterned mask 424, as shown in FIG. 4D. In various embodiments,alternatively or additionally, an isotropic etching may be executed, forexample by means of wet chemical etching. This may lead to an inner rim537 of the material 422 and/or 422 b, as shown in FIG. 6A and FIG. 8A,that is etched beyond being flush with the inner rim 419 of thepatterned mask 424. In other words, after the isotropic etching, theinner rim 537 of the material 422 may be located between the anothersurface 425 of the patterned mask 424 and the front side structure 429.

In various embodiments, the pattern of the patterned mask 424 may beformed in such a way that it can fulfill two functions: Firstly, thepatterned mask 424 may serve as the patterned mask 424 for forming thesecond opening 536 in the material 422, for example the inner rim 419 ofthe patterned mask 424 may be located such that the second opening 536may be formed in the material 422 from the first opening 532, forexample by means of etching, and the second opening 536, with itsstructure and position defined by the patterned mask 424, may bepositioned in the desired relative position with respect to thestructure of the first layer 428 and/or the second layer 430. Andsecondly, the patterned mask may serve as a stop for the forming of thefirst opening 532, for example as an etch stop when the first opening532 is formed by means of etching, for example by means of plasmaetching, Bosch etching or wet-chemical etching. This means that theouter rim 421 of the patterned mask 424 may be positioned in such a wayas to ensure that the line where the virtual planes along the side walls535 of the first opening 532 cross the first side of the carrier 420 islocated adjacent to (in FIG. 4D underneath) the patterned mask 424, andnot adjacent to the material 422, even if the above described effectslike tilting, shape change etc. occur during the forming of the firstopening 532. In other words, a size of the patterned mask 424 orthogonalto its thickness may define a region in which the stop for the formingof the first opening 532, for example the etch stop, exists.

In various embodiments, the thickness a of the material 422 may be muchsmaller than the thickness b of the carrier 420, for example the ratioof the thickness of the carrier 420 and the material 422 may be above10, for example above 100, for example about 200. In variousembodiments, it may be possible to create an opening at the first layer428 and/or the second layer 430 from the second side 427 of the carrier420 without having to define the exact opening to be created in thesecond mask 533, which would cause large deviations from the desiredshape of the opening at the first layer 428 and/or the second layer 430because of the large depth of the first opening 532. Instead, theopening to be formed at the first layer 428 and/or the second layer 430may be defined by the patterned mask 424, and the opening to be formednear the first layer 428 and/or the second layer 430 may be the secondopening 536 with its relatively shallow depth. In this way, a largelateral displacement may be avoided, and the opening may be formed inalmost exactly the desired position. If, for example, a tilting occurredduring the forming of the second opening 536 with an angle that is thesame as the angle with which the first opening 532 may be tilted, afactor by which the lateral displacement of the first opening 532 islarger than the lateral displacement of the second opening 536 may bethe ratio of the thickness b of the carrier 420 and the thickness c ofthe material 422. If, for example, a lateral displacement of about 1 μmoccurred in an opening structure during the forming of a first opening532 in a carrier 420 with a thickness of about 400 μm because of atilting of about 0.143°, a tilting with the same angle occurring duringthe forming of a second opening in a material 422 of the openingstructure, wherein the material may have a thickness of about 2 μm,would lead to a lateral displacement of only about 50 nm. This meansthat, by using the patterned mask 424, which may be located near thesecond surface of the material 422, compared with the second mask 533,as the mask for forming the second opening 536, a relative positioningof the structures of the first layer 428 and/or the second layer 430with respect to the second opening 536 may be achieved with a very highprecision.

With the patterned mask 424 having been formed over the first side 426of the carrier 420, the inner rim 419 of the patterned mask 424 mayrepresent a smooth edge that may serve as a patterned mask 424 forforming a smooth inner rim 537 on the second part 422 b of the material422 in the second opening 536, even though the edge 535 of the carrier420 along the first opening 532 may be a rough edge.

As another way to describe the method, the patterned mask 424 and thesecond mask 533 may be considered as forming a kind of “focusingsystem”, which allows for forming an upper edge of the second opening536 at a desired position with high precision, while at the same timeallowing for rather loose tolerances on the position and/or shape of thefirst opening 532 and of the second mask 533, respectively.

In various embodiments, the method may thus include forming thepatterned mask 424 over the first side 426 of the carrier 420, formingthe material 422 over the first side 426 of the carrier 420 covering atleast a portion of the carrier 420, forming the second mask 533 over thesecond side 427 of the carrier 420 opposite the first side 426 of thecarrier 420, and forming an opening 532, 536 in the carrier 420 and inthe material 422 from the second side 427 of the carrier 420 using thesecond mask 533 and the patterned mask 424 as masks. A positioningtolerance and/or a shape tolerance on the second mask 533 may be looserthan on the patterned mask 424.

FIG. 5A to FIG. 5H show a process flow for a method for forming anopening structure 600 in accordance with various embodiments. Unlessspecifically excluded, materials, thicknesses and sizes of structures,techniques of forming a layer, an opening or a structure and otherparameters may be the same as described in context with correspondingfeatures in FIG. 4A to FIG. 4D.

As shown in FIG. 5A, the method for forming an opening structure 600 inaccordance with various embodiments may include forming a patterned mask424 over a first side 426 of a carrier 420. This may include depositinga mask material, for example an oxide, for example tetraethylorthosilicate (TEOS) over the first side 426 of the carrier 420.

In various embodiments, the material used for forming the patterned mask424 may additionally be used for forming an alignment mark 644 over thefirst side of the carrier 420. In various other embodiments, thealignment mark 644 may be formed over the first side 426 of the carrier420 before or after the forming of the patterned mask 424, for exampleusing a different material.

In various embodiments, a thickness of the material of the patternedmask 424 deposited over the first side 426 of the carrier 420 may bechosen such that a desired thickness of the patterned mask 424 mayremain even after CMP is applied to the patterned mask 424. Thethickness may for example be around 850 nm.

In various embodiments, the TEOS may be densified.

In various embodiments, the material of the patterned mask 424 formedover the first side of the carrier 420 may be patterned, for example byphotolithographical patterning, i.e. a pattern defined by a photoresistmay be formed in the material of the patterned mask 424. Forming thepattern in the material of the patterned mask 424 may for example beperformed by means of etching, e.g. plasma etching. Thereafter, thephotoresist may be removed, for example by means of photochemicaletching, plasma etching, plasma ashing, and/or wet chemical etching.

In various embodiments, as shown in FIG. 5B, the method may furtherinclude forming material 422 over the first side 426 of the carrier 420covering at least a portion of the carrier 420. The material 422 may forexample be formed by means of deposition. The material 422 may forexample be polysilicon, or for example amorphous silicon. The material422 may be doped in situ.

In various embodiments, the material used for forming the material 422,e.g. the polysilicon, may also be used for forming a second backsidelayer 648 over the first backside layer 640.

In various embodiments, a thickness of the material 422 may be such thatthe patterned mask and the material, and possibly also the alignmentmark, may form one common surface after CMP from the side of thematerial 422 over the first side 426 of the carrier 420 down to the mask424. The thickness of the material may at least be the desired thicknessof the mask 424 after CMP, for example the same as the thickness withwhich the patterned mask 424 is formed, or it may be thicker.

In various embodiments, the material 422 may be formed also over thepatterned mask 424, and/or over the alignment mask 644. In variousembodiments, the material 422 may be formed only over/on the carrier420, and not over the patterned mask 424 or the alignment mark 644.

As shown in FIG. 5C, the method may further include chemical-mechanicalpolishing/planarization from the side of the material 422 over the firstside 426 of the carrier 420 down to the patterned mask 424 until anothersurface 425 of the patterned mask 424 (and, if present, a correspondingsurface of the alignment mark 644) is/are exposed and/or a desired levelof polishing/planarization and/or a desired thickness of the mask 424,and/or a pre-defined duration of CMP is reached. The patterned mask 424may have been formed thick enough to allow for a thinning by means ofthis CMP.

In various embodiments, as shown in FIG. 5D, the method may furtherinclude forming an alignment mark etching mask 650 over the patternedmask 424 and/or over the material 422. The alignment mark etching mask650 may for example be formed from photoresist. The alignment mark 644may be removed, for example by means of wet chemical oxide etching.

In various other embodiments, for example if the alignment mark 644 isformed from a material different from the material of the patterned mask424, for example if said material has a different removalcharacteristics, e.g. etching characteristics, from both the material422 and the material of the patterned mask 424, the alignment mark 644may be removed, e.g. etched, without forming the alignment mark etchingmask 650.

In various embodiments, as shown in FIG. 5F, the method may furtherinclude forming a second part 422 b of the material 422 over thematerial 422, and possibly also above the patterned mask 424 and/or thecarrier 420, in a region where the alignment mark 644 was removed. Thematerial of the second part 422 b of the material 422 may be the same asthe material 422, or it may be a different material, for example amaterial with similar properties as the material 422, for example withsimilar physical, chemical, mechanical and/or electrical properties, forexample with a similar coefficient of thermal expansion and/or withsimilar removal characteristics, e.g. etching characteristics. Thematerial of the second part 422 b of the material 422 may for example bedoped in situ. In this way, an intrinsic stress (which might bow thecarrier 420) after a later heating may be avoided, and a good electricalconnectivity to the carrier 420 may be provided. The forming of thesecond part 422 b of the material 422 may include deposition, forexample deposition of polysilicon or of amorphous silicon. The secondpart 422 b of the material 422 (or, more generally, over the material422) may have any thickness that is required by a front side structure761 (see FIG. 5H) to be formed over the second part 422 b of thematerial 422 (or, more generally, over the material 422). In variousembodiments, a rigid body may be provided by a thick material 422 (and,if present, 422 b). In various embodiments, the front side structure 761may require a pre-defined depth of an opening (for example correspondingto the second opening in FIG. 4D, or a combination of the first opening532 and the second opening 536 in FIG. 4D). For example, the second part422 b of the material 422 may have a thickness in a range from about 500nm to about 3 μm, for example from about 1 μm to about 1.5 μm, forexample around 1.4 μm. In various embodiments, in which the second part422 b of the material 422 is also formed in the region where thealignment mark 644 was removed, a width x of the alignment mark 644 (seeFIG. 5A) and the thickness of the second part 422 b of the material 422may be selected in such a way that the region where the alignment mark644 was removed does not get completely filled in by the second part 422b of the material 422. In other words, the width of the alignment mark644 may be determined to be large enough and/or the thickness of thesecond part 422 b of the material 422 may be selected to be thin enoughsuch that a position where the alignment mark 644 had been placed can beidentified even after the forming of the second part 422 b of thematerial 422, e.g. by means of a cavity remaining at or above theposition where the alignment mark 644 had been placed.

In various embodiments, for example if the material 422 and/or thesecond part 422 b of the material 422 are formed from polysilicon orfrom amorphous silicon, the material 422 and/or the second part 422 b ofthe material 422 may be crystallized, for example by means of thermalannealing (heating).

A front side structure 761 (as shown in FIG. 5H and FIG. 6A, andcorresponding to the front side structure 429 in FIG. 4D) may forexample include or consist of a microphone or a loudspeaker, a membrane762 for a microphone or for a loudspeaker, or a membrane 762 with aholding structure 758, 760. In various embodiments, the membrane 762 mayessentially be a plane membrane. In various other embodiments, themembrane 762 may include a corrugation 752. In various embodiments, asshown in FIG. 5G, which shows a region indicated by vertical lineslabelled A and A′ in FIG. 5F after further processing, the corrugation752 may be formed in the second part 422 b of the material 422, therebyproviding a form or a mold for the corrugation 752 to be formed in themembrane 762. A positioning of the corrugation 752. in a plane of thematerial in which it is formed, i.e. in the second part 422 b of thematerial 422 or the material 422, may be accurately adjusted by means ofthe alignment mark 644 or by the cavity remaining at or above theposition where the alignment mark 644 had been placed. In variousembodiments, for example if no dedicated alignment mark is required, forexample because the patterned mask 424 may be used for ensuring theaccurate positioning of the corrugation 752, or generally of the frontside structure 429 (as in FIG. 4D), the corrugation 752 may be formed inthe material 422, or more generally, the front side structure 429 may beformed above or in the material 422.

In various embodiments, the forming of the corrugation 752 may include alocal oxidization of silicon, i.e. of the second part 422 b of thematerial 422 or of the material 422, an etching of the corrugation 752,and a removal of the oxide (not shown).

In various embodiments, as shown in FIG. 5H, the forming of the frontside structure 761 may further include forming of a first layer 758 overthe second part 422 b of the material 422, of an intermediate layer 760over the first layer 758, and of a second layer 762 (also referred to asthe membrane 762) over the intermediate layer 760.

In various embodiments, the forming of the first layer 758 may forexample include forming an oxide layer, for example by means of rapidthermal oxidization. In various embodiments, the first layer 758 mayserve as a diffusion barrier for the intermediate layer to prevent oralleviate out-diffusion from the intermediate layer, for example if theintermediate layer 760 is formed from borophosphosilicate glass. Thefirst layer 758 may have a thickness in a range from about 1 nm to about1 μm, for example from about 100 nm to about 500 nm.

In various embodiments, the forming of the intermediate layer 760 mayfor example include forming a borophosphosilicate glass layer, forexample by means of deposition. In various embodiments, the intermediatelayer 760 may be made flow, for example by means of heating above aflowing point. The intermediate layer 760 may be formed as thin aspossible while providing sufficient stability. For example, theintermediate layer may have a thickness in a range from about 100 nm toabout 300 nm, for example about 150 nm.

In various embodiments, the forming of the second layer 762 may includeforming an oxide layer, for example by means of deposition, for exampleby means of TEOS deposition or by means of plasma deposition. In thisvarious embodiments, the second layer 762 may have a thickness in arange from about 50 nm to about 1 μm, for example from about 300 toabout 700 nm, for example about 330 nm or about 660 nm.

In various embodiments, the method may include various furtherprocessing, e.g. forming of a first opening 532 and a second opening 536as described in connection with FIG. 4C and FIG. 4D, and with FIG. 6Aand FIG. 6B.

FIG. 6A and FIG. 6B show cross sections of an opening structure 600according to various embodiments, and at different stages during amanufacturing process.

In various embodiments, the opening structure 600 may include a carrier420 including a first side 426 and a second side 427 opposite the firstside 426; a patterned mask 424 formed over the first side 426 of thecarrier 420; a first opening 532 formed in the carrier 420, wherein thefirst opening 532 extends between the first side 426 of the carrier 420and the second side 427 of the carrier 420, and wherein the firstopening 532 is at least partially covered at a first end of the firstopening 532 by the patterned mask 424; a material 422, formed over atleast a part of the carrier 420 on the first side 426 of the carrier420; and a second opening 536 formed in the material 422 in fluidcommunication with the first opening 532.

The opening structure 600 may have been formed by employing a methodaccording to various embodiments described in connection with FIG. 4A toFIG. 4D, FIG. 5A to FIG. 5H or FIG. 7A to FIG. 7E. In variousembodiments, the opening structure may include features described incontext with said methods of its manufacturing, and vice versa.

In various embodiments, the opening structure 600 may have undergonefurther processing, at least some of which will be described in thefollowing.

In various embodiments, the opening structure 600 may further include asecond part 422 b of the material 422, which may be formed at leastpartially over the material 422. The second part 422 b of the material422 may additionally be formed at least partially over the patternedmask 424. In various embodiments, the second part 422 b of the material422 may be formed together with the material 422. In this case, thematerial 422 and the second part 422 b of the material 422 may togetherbe considered as forming the material 422.

In various embodiments, the opening structure 600 may further include afront side structure 761 formed at least partially over the second part422 b of the material 422, and/or over the material 422. The front sidestructure 761 may additionally be formed at least partially over thepatterned mask 424. In various embodiments, the front side structure 761may include a first layer 758. The front side structure 761 may includean intermediate layer 760 and/or a second layer 762.

In various embodiments, the accurately shaped and positioned patternedmask 424 may have an inner rim 419 that may represent a smooth edge. Thepatterned mask 424 with its inner rim 419 may serve as a mask forforming a smooth inner rim 537 on the second part 422 b of the material422 in the second opening 536, even though the edge 535 of the carrier420 may be a rough edge.

In various embodiments, in the opening structure 600, the second part422 b of the material 422 may not be electricaly floating, it may ratherbe in electrical contact with the carrier 420 and therefore have anelectrical potential of the carrier 420. Consequently, additionalprocesses, e.g. photolithographical processes, for electricallycontacting the second part 422 b of the material 422 may not berequired.

In various embodiments, the second part 422 b of the material 422 may beas thick as desired, e.g. as thick as required by an intendedapplication. Nevertheless, this may be accomplished without introducingadditional topology.

In various embodiments, the second part 422 b of the material 422 may becut/sawed jointly with the carrier 420. By way of example, the carrier420 may be cut together with the material 422 and/or with the secondpart 422 b of the material 422. Cutting of the opening structure 600 mayfor example be performed by means of laser cutting/sawing. The openingstructure 600 may be suitable for laser cutting, because the material422 and the second part 422 b of the material 422 may be similar to thematerial of the carrier 420 or may be the same material as the materialof the carrier 420. The cutting may be performed vertically to the firstside 426 and/or the second side 427 of the carrier 420. The cutting mayfor example be performed in a region where the opening structure 600 maybe cut vertically to the first side 426 and/or the second side 427 ofthe carrier 420 without cutting through the patterned hard mask 424and/or through the front side structure 761 and/or through the firstopening 532 and/or through the second opening 536.

Chemical-mechanical polishing may be performed before forming the frontside structure 761. The front side structure 761, for example amicroelectromechanical system, for example a membrane with or without acorrugation, may be formed in the opening structure 600 without havingto account for a later chemical-mechanical polishing.

As shown in FIG. 6B, in various embodiments, the opening structure 600may further include a third opening 872. The third opening 872 may beformed from a direction of the second opening 536, and it may be influid communication with the second opening 536. The second part 422 bof the material 422 may serve as a patterned mask for forming the thirdopening 872. An inner rim 537 of the second part 422 b of the material422 may be smooth. It may have been smoothly formed when the secondopening 536 was formed using the patterned mask 424 as a mask. Thesecond part 422 b of the material 422 may have been patterned with anaccurate shape and positioning with respect to the front side structure761. It may serve for forming a smooth, accurately aligned and shapededge

In various embodiments, forming of the third opening 872 may for examplebe performed by means of etching, for example by means of plasma etchingor wet-chemical etching, for example by means of etching using hydrogenfluoride or hydrofluoric acid.

In various embodiments, the first layer 758 and the patterned mask 424may be reduced in volume, e.g. etched, during the forming of the thirdopening 872. The intermediate layer 760 may also be reduced in volume,e.g. etched, during the forming of the third opening 872. Thereby, a newinner rim 876 may be formed on the patterned mask 424, the first layer758 may newly form an inner rim 874, and the intermediate layer 760 maynewly form an inner rim 878. In various embodiments, a positioning ofthe inner rim 874 of the first layer 758 and of the inner rim 878 of theintermediate layer 760 may depend on the front side structure 761, andits intended functionality and positioning. But generally, the innerrims 874 and/or 878 should not recede so far that the front sidestructure 761 or essential parts of the front side structure 761 becomedetached from the opening structure 600. In other words, the thirdcavity 872 should at least be formed small enough such that the frontside structure 761, or at least those parts that are essential to thefunctionality of the opening structure 600, may remain physicallyconnected to the opening structure 600. For example, the second layer762 of the front side structure 761 may form a membrane 762 that issupported near its edge by parts of the first layer 758 and/or theintermediate layer 760 that remain outside their respective inner rims874 and/or 878, forming a supporting structure. In various embodiments,the front side structure 761 may include structures that may have to becleared in order to ensure functionality of the front side structure761. In case of the membrane 762, such structures may for exampleinclude a vent hole 868 or the corrugation 752. In that case, the thirdcavity 872 may be formed in such a way, e.g. large enough and with theinner rims 874 and/or 878 receding far enough from a center of the thirdcavity 872, to ensure that said structures are freed from material thathinders their proper functioning. In various embodiments as shown inFIG. 6A, this may mean that the first layer 758 and the second layer 760are removed completely underneath the corrugation 752 and underneath thevent hole 868.

In various embodiments, within their inner rims 874 and/or 878, thefirst layer 758 and/or the intermediate layer 760, respectively, mayform the third cavity 872. The third cavity 872, the second cavity 536and the first cavity 532 may be in fluid communication. They may formone joint more or less free room underneath at least a part of the frontside structure 761, i.e. on a side of the front side structure 761 thatmay be facing towards the carrier 420 In various embodiments, forexample if the front side structure 761 includes the membrane 762, thethird cavity 872, the combination of third cavity 872 and second cavity536, or the combination of third 872, second 536 and first 532 cavitymay provide free space that may make a movement of the membrane 762 intoand out of the cavity or cavities possible. In various embodiments, thisfree space may similarly be provided to front side structures 761 thatmay require space for motion, a resonance volume, an evacuated orfluid-filled volume, or the like.

In various embodiments, a distance between an inner rim 537 of thesecond part 422 b of the material 422 and an inner rim 874 of the firstlayer 758, a thickness of the first layer 758, a thickness of theintermediate layer 760, a size/diameter of the inner rim 874 of thefirst layer 758 and parameters relevant for the movement of a moveablepart of the front side structure 761 may be chosen such that aprotruding part of the second part 422 b of the material 422, which mayprotrude into the second opening 536, may not hinder the movement of themoveable part of the front side structure 761 and/or damage it.

FIG. 7A to FIG. 7E show a process flow for a method for forming anopening structure in accordance with various embodiments. Unlessspecifically excluded, materials, thicknesses and sizes of structures,techniques of forming a layer, an opening or a structure and otherparameters may be the same as described in context with correspondingfeatures in FIG. 4A to FIG. 4D, FIG. 5A to 5H or FIG. 6A or FIG. 6B.

As shown in FIG. 7A, the method for forming an opening structure inaccordance with various embodiments may include forming a patterned mask424 over a first side 426 of a carrier 420. This may include depositinga mask material, for example an oxide, for example tetraethylorthosilicate (1E0S) or a thermal oxide, over the first side 426 of thecarrier 420.

In various embodiments, a thickness of the material of the patternedmask 424 deposited over the first side 426 of the carrier 420 may forexample be 650 nm.

In various embodiments, the TEOS may be densified.

In various embodiments, the material of the patterned mask 424 formedover the first side of the carrier 420 may be patterned, for example byphotolithographical patterning, i.e. a pattern defined by a photoresistmay be formed in the material of the patterned mask 424. Forming thepattern in the material of the patterned mask 424 may for example beperformed by means of etching, e.g. plasma etching, which may leave thefirst backside layer 640 intact. Thereafter, the photoresist may beremoved, for example by means of photochemical etching , plasma etching,plasma ashing and/or wet chemical etching.

In various embodiments, as shown in FIG. 7B, the method may furtherinclude forming material 422 over the first side 426 of the carrier 420covering at least a portion of the carrier 420, and over the patternedmask 424. The material 422 may for example be formed by means ofdeposition or SEG. The material 422 may for example be silicon, forexample polysilicon, or amorphous silicon. The material 422 may be dopedin situ, such that a heating of the opening structure may not createstress within the material 422, and for providing a good electricalcontact to the carrier 420.

In various embodiments, a thickness of the material 422 may be such thatthe material 422 may undergo CMP from the side of the material 422 overthe first side 426 of the carrier 420, but leave at least a thin layerof the material 422 over the patterned mask 424. In other words, thethickness of the material 422 may at least be the sum of the thicknessof the patterned mask 424 and the thickness of the thin layer of thematerial 422. The thickness of the material 422 may for example be 1100nm.

In various embodiments, an alignment mark 979 may be formed in thematerial 422 and in the carrier 420 from the material 422 above thefirst side 426 of the carrier 420. The alignment mark 979 may be anopening, for example a cavity or a trench. The alignment mark 979 may beformed by means of etching, for example by means of plasma etching, forexample by means of isotropic etching. The etching may be performedphotolithographically, for example by using a photo mask (not shown).

A depth d and a width x′ of the alignment mark 979 may depend on thethickness of the material 422 b. A thick material 422 b may fill thealignment mark 979, such that it may not be recognized as alignmentmark. Thus, the depth d and the width x′ of the alignment mark 979 maybe selected such that the alignment mark 979 may not get filled in bythe material 422 b with the intended thickness. In various embodiments,the width of the structure in the photo mask that will be used forforming the alignment mark 979 may correlate with the thickness of thematerial 422 b, i.e. if the material 422 b is thicker, the alignmentmark 979 may be formed wider and/or deeper, and if the material 422 b isthinner, the alignment mark 979 may be formed narrower and/or shallower.In various embodiments, the alignment mark 979 may have a depth of about600 nm and a width of about 4 μnm. In other embodiments, the alignmentmark may have any combination of keeping that depth or width, making thealignment mark 979 deeper or shallower, and making it narrower or wider.

In various embodiments, the photo mask may be removed.

As shown in FIG. 7C, in various embodiments, the opening structure 900may be polished from the side of the material 422, for example by meansof CMP. A smooth, plane surface of the material 422 may be formed, forexample over the patterned mask 424 and over the material 422. Athickness of the material 422 over the carrier 420 after polishing maybe larger than the thickness of the patterned mask 424, for example thethickness of the material 422 over the carrier 420 may be about 900 nm.

In various embodiments, as shown in FIG. 7C, the method may furtherinclude forming a second part 422 b of the material 422 over thematerial 422, and over the carrier 420 in a region where the alignmentmark 979 was formed, possibly also above the patterned mask 424. Thematerial of the second part 422 b of the material 422 may be the same asthe material 422, or it may be a different material, for example amaterial with similar properties as the material 422, for example withsimilar physical, chemical, mechanical and/or electrical properties, forexample with a similar coefficient of thermal expansion and/or withsimilar removal characteristics, e.g. etching characteristics. Thematerial of the second part 422 b of the material 422 may for example bedoped in situ. In this way, an intrinsic stress (which might bow thecarrier 420) after a later heating may be avoided, and a good electricalconnectivity to the carrier 420 may be provided. The forming of thesecond part 422 b of the material 422 may include deposition, forexample deposition of silicon, for example of polysilicon or ofamorphous silicon. The second part 422 b of the material 422 (or, moregenerally, over the material 422) may have any thickness that isrequired by a front side structure 761 (see FIG. 5H) to be formed overthe second part 422 b of the material 422 (or, more generally, over thematerial 422). In particular, in various embodiments a rigid body may beprovided by a thick material 422 (and, if present, 422 b). This may actlike a thick carrier 420.

In various embodiments, a breaking of the front side structure 429 on arough edge of a carrier around a cavity, like it may happen in anopening structure of the prior art if it suffers an impact, may beavoided.

In various embodiments, the front side structure 761 may require apre-defined depth of an opening (for example corresponding to the secondopening in FIG. 4D, or a combination of the first opening 532 and thesecond opening 536 in FIG. 4D). By way of example, the second part 422 bof the material 422 may have a thickness in a range from about 500 nm toabout 3 μm, for example from about 1 μm to about 1.5 μm, for examplearound 1.4 μm. In various embodiments, in which the second part 422 b ofthe material 422 is also formed in the region where the alignment mark979 was formed, a width x′ of the alignment mark 979 (see FIG. 7B) andthe thickness of the polished/planarized material 422 and of the secondpart 422 b of the material 422 may be selected in such a way that theregion where the alignment mark 979 was formed does not get completelyfilled in by the second part 422 b of the material 422. In other words,the width of the alignment mark 979 may be determined to be large enoughand/or the thickness of the second part 422 b of the material 422 may beselected to be thin enough such that a position where the alignment mark979 is located can be identified even after the forming of the secondpart 422 b of the material 422, e.g. by means of a cavity remaining ator above the position where the alignment mark 979 was formed.

In various embodiments, for example if the material 422 and/or thesecond part 422 b of the material 422 are formed from polysilicon orfrom amorphous silicon, the material 422 and/or the second part 422 b ofthe material 422 may be crystallized, for example by means of thermalannealing (heating).

In various embodiments, a corrugation 752, or rather a form or a moldfor the corrugation 752 to be formed in the membrane 762, may be formedaccording to processes described in the context of FIG. 5G, and with thesame reasoning, materials, parameters, results etc. As an alignmentmark, the alignment mark 979, or the cavity remaining at or above theposition where the alignment mark 979 had been, may be used.

As shown in FIG. 7E, the method for forming the opening structure 900may, in various embodiments, further include forming a front sidestructure 761.

In various embodiments, the front side structure 761 may be formed inthe same way and with the same processes, parameters, materials etc. asdescribed in the context of FIG. 5H.

In various embodiments, the method may include various furtherprocessing, e.g. forming of a first opening 532 and a second opening 536as described in connection with FIG. 4C and FIG. 4D, FIG. 6A and FIG.6B, and FIG. 8A and FIG. 8B.

FIG. 8A and FIG. 8B show cross sections of an opening structure 900according to various embodiments, and at different stages during amanufacturing process. The opening structure 900 may have been formed byemploying a method according to various embodiments described inconnection with FIG. 4A to FIG. 4D, FIG. 5A to FIG. 5H, FIG. 7A to FIG.7E, FIG. 8A and/or FIG. 8B. In various embodiments, the openingstructure 900 may include features described in context with saidmethods of its manufacturing, and vice versa.

In various embodiments, the opening structure 900 may have undergonefurther processing after the stage shown in FIG. 7E, at least some ofwhich may correspond to those described in context with processingapplied to the opening structure 600, for example in context with FIG.6A and FIG. 6B.

In various embodiments, the opening structures 600 of FIG. 6A and FIG.6B may differ from the opening structures 900 of FIG. 8A and FIG. 8B bya thin layer of material 422 formed over the patterned mask 424 whichmay be present in the opening structure 900, and not be present in theopening structure 600. In various embodiments, where the material 422and the second part of the material 422 b may be the same material, thisdifference may not be noticeable in the opening structures 600 and 900,respectively, but may only be noticed in the method for manufacturingthe opening structures 600 and 900, respectively. Additionally, theopening structures 600 and 900 may differ by the alignment marks 644 and979, respectively, which are not shown in FIG. 6A, FIG. 6B, FIG. 8A andFIG. 8B.

FIG. 9 shows a schematic diagram of a method for forming an openingstructure in accordance with various embodiments.

In various embodiments, the method may include, in 1272, forming apatterned mask over a first side of a carrier. It may further include,in 1274, forming material over the first side of the carrier covering atleast a portion of the carrier. The method may further include, in 1276,forming a first opening into the carrier from a second side of thecarrier opposite the first side of the carrier to at least partiallyexpose a surface of the patterned mask. It may further include, in 1278,forming a second opening into the material from the second side of thecarrier using the patterned mask as a mask.

In various embodiments, the method may include further processing, forexample according to various embodiments described in context with FIG.4A to FIG. 4D, FIG. 5A to FIG. 5H, FIG. 6A, FIG. 6B, FIG. 7A to FIG. 7E,FIG. 8A and FIG. 8B.

FIG. 10A to FIG. 10D show a process flow for a method for forming anopening structure 1300 and an opening structure 1300 in accordance withvarious embodiments.

In various embodiments, as shown in FIG. 10A, the method may includeforming at least one opening 1380 in a carrier 420 from a first side 426of the carrier. The carrier 420 may have the same properties as thecarrier 420 of any of the previously described embodiments. In variousembodiments, the at least one opening 1380 may be formed by means ofetching, for example by means of plasma etching.

In various embodiments, a depth of the at least one opening 1380 may beapproximately the same as a height of a structured mask 424 to beformed, wherein the structured mask 424 to be formed may be similar tothe structured mask 424 of the previously described embodiments, withthe exception that the structured mask 424 in accordance with variouspresently described embodiments may be formed within the carrier 420,while the structured mask 424 of the previous embodiments was formed onthe carrier 420.

In various embodiments, a number, location and shape of the at least oneopening 1380 may correspond to a shape of the structured mask 424 to beformed. In various embodiments, the structured mask 424 to be formed,and hence the opening 1380, may be shaped like an annulus.

In various embodiments, as shown in FIG. 10B, a material 424 may beformed over the carrier 420 from the first side 426 of the carrier 420.Material, parameters, of the material 424, methods used for applying thematerial 424 etc. may be the same as those of the patterned mask 424 ofthe previous embodiments.

In various embodiments, as shown in FIG. 10C, a portion of the material424 may be removed. The portion of the material 424 may for example beremoved by means of etching, and/or by means of chemical-mechanicalpolishing. In various embodiments, the removal of the portion of thematerial 424 may be performed in such a way that a smooth surface,including a surface of the carrier 420 on the first side 426 of thecarrier 420 and a surface of the material 424 remaining in the at leastone opening 1380, may be formed. In this way, a patterned mask 424 mayhave been formed within the carrier 420.

In various embodiments, a material 422 b may be formed over the carrier420 and the patterned mask 424 from the first side 426 of the carrier420. Material, parameters, of the material 422 b, methods used forapplying the material 422 b etc. may be the same as those of thematerial 422 b of the previous embodiments.

After the forming of the material 422 b, the method for forming anopening structure 1300 may continue in similar ways to the methods forforming the opening structures in previous embodiments, for example themethod for forming an opening structure 1300 may be followed byprocesses described in the context of FIG. 4B to FIG. 4D, and/or byprocesses described in the context of FIG. 5G and FIG. 5H, and/or byprocesses described in the context of FIG. 7D and FIG. 7E.

In various embodiments the opening structure 1300 shown in FIG. 10D maybe formed using processes described in context with FIG. 10A to FIG.10C. The opening structure may differ from the opening structures 600and 900 shown in FIG. 6B and FIG. 8B, respectively, mainly in that thematerial 422 of the opening structures 600 and 900 is missing in theopening structure 1300. The carrier 420 of the opening structure 1300may extend to a region in which the material 422 would be located in anopening structure according to opening structures 600 or 900.

FIG. 11A to FIG. 11C show a process flow for a method for forming anopening structure 1400 and the opening structure 1400 in accordance withvarious embodiments.

In various embodiments, as shown in FIG. 11A, the method may includeforming a material 424 for a patterned mask 424 in and over a carrier420 from a first side 426 of the carrier 420. The carrier 420 may havethe same properties as the carrier 420 of any of the previouslydescribed embodiments. In various embodiments, the carrier 420 may forexample include or consist of silicon.

In various embodiments, the material 424 may be formed in and over thecarrier 420 by means of a local oxidization of silicon (a so-calledLOCOS-process). The forming of the material 424, in this case theoxidization of the carrier 420 in pre-defined regions located on thefirst side 426 of the carrier 420, may continue until the material 424—asilicon dioxide formed by means of the oxidization—extends to a depthinto the carrier 420 that corresponds to a height of a structured mask424 to be formed. The structured mask 424 to be formed may be similar,for example also in shape, to the structured mask 424 of the previouslydescribed embodiments, with the exception that the structured mask 424in accordance with various presently described embodiments may be formedwithin the carrier 420, while the structured mask 424 of the previousembodiments was formed on the carrier 420. In this respect, thestructured mask 424 of the presently described embodiments may besimilar to the structured mask 424 of the opening structure 1300.

In various embodiments, as shown in FIG. 11B, a portion of the material424 may be removed. The portion of the material 424 may for example beremoved by means of etching, and/or by means of chemical-mechanicalpolishing. In various embodiments, the removal of the portion of thematerial 424 may be performed in such a way that a smooth surface,including a surface of the carrier 420 on the first side 426 of thecarrier 420 and a surface of the material 424 remaining in the at leastone opening 1380, may be formed. In this way, a patterned mask 424 mayhave been formed within the carrier 420.

In various embodiments, a material 422 b may be formed over the carrier420 and the patterned mask 424 from the first side 426 of the carrier420. Material, parameters, of the material 422 b, methods used forapplying the material 422 b etc. may be the same as those of thematerial 422 b of the previous embodiments.

After the forming of the material 422 b, the method for forming anopening structure 1400 may continue in similar ways to the methods forforming the opening structures in previous embodiments, for example themethod for forming an opening structure 1400 may be followed byprocesses described in the context of FIG. 4B to FIG. 4D, and/or byprocesses described in the context of FIG. 5G and FIG. 5H, and/or byprocesses described in the context of FIG. 7D and FIG. 7E.

In various embodiments the opening structure 1400 shown in FIG. 10D maybe formed using processes described in context with FIG. 10A to FIG.10C. The opening structure may differ from the opening structures 600and 900 shown in FIG. 6B and FIG. 8B, respectively, mainly in that thematerial 422 of the opening structures 600 and 900 is missing in theopening structure 1300. The carrier 420 of the opening structure 1400may extend to a region in which the material 422 would be located in anopening structure according to opening structures 600 or 900. In thisrespect, the opening structure 1400 may be similar to the openingstructure 1300.

FIG. 12 shows a schematic diagram of a method for forming an openingstructure in accordance with various embodiments.

In various embodiments, the method may include, in 1572, forming apatterned mask in a carrier from a first side of a carrier. It mayfurther include, in 1574, forming material over the first side of thecarrier covering at least a portion of the carrier. The method mayfurther include, in 1576, forming a first opening into the carrier froma second side of the carrier opposite the first side of the carrier toat least partially expose a surface of the patterned mask. It mayfurther include, in 1578, forming a second opening into the materialfrom the second side of the carrier using the patterned mask as a mask.

In various embodiments, the method may include further processing, forexample according to various embodiments described in context with FIG.4A to FIG. 4D, FIG. 5A to FIG. 5H, FIG. 6A, FIG. 6B, FIG. 7A to FIG. 7E,FIG. 8A and FIG. 8B.

In various embodiments, a method for manufacturing an opening structureis provided. The method may include: forming a patterned mask over afirst side of a carrier; forming material over the first side of thecarrier covering at least a portion of the carrier; forming a firstopening in the carrier from a second side of the carrier opposite thefirst side of the carrier to at least partially expose a surface of thepatterned mask; and forming a second opening in the material from thesecond side of the carrier using the patterned mask as a mask.

In various embodiments, forming material over the first side of thecarrier may include forming material over the first side of the carriercovering at least a portion of the carrier and at least a portion of thepatterned mask. In various embodiments, the material may be configuredto have similar removal characteristics as the material of the carrier.In various embodiments, forming the patterned mask over the first sideof the carrier may comprise forming a patterned hard mask. In variousembodiments, the material of the carrier and the material may includethe same material. In various embodiments, the material of the carriermay include silicon. In various embodiments, the material may includesilicon. In various embodiments, the material may include polysilicon.In various embodiments, the first opening may be formed into the carriersuch that at least a portion of a first mask portion of the patternedmask and at least a portion of a second mask portion of the patternedmask are exposed by the first opening. In various embodiments, at leastone of the first opening and the second opening may be formed by meansof an etching process. In various embodiments, at least one of the firstopening and the second opening may be formed by means of a plasmaetching process. In various embodiments, at least one of the firstopening and the second opening may be formed by means of a wet etchingprocess. In various embodiments, the first opening may be formed to havea larger width than the second opening. In various embodiments, themethod may further include forming a front side structure over the firstside of the material. In various embodiments, forming the front sidestructure may include forming at least one of a mechanical component andan electronic component over the first side of the material. In variousembodiments, the method may further include forming a microphonecomprising at least one of a group comprising the mechanical componentand the electronic component. In various embodiments, at least one ofthe first opening and the second opening may be a trench.

In various embodiments, a device is provided. The device may include thefeatures of: a carrier including a first side and a second side oppositethe first side; a patterned mask formed over the first side of thecarrier; a first opening formed in the carrier, wherein the firstopening may extend between the first side of the carrier and the secondside of the carrier, and wherein the first opening may be at leastpartially covered at a first end of the first opening by the patternedmask; a material formed over the carrier on the first side of thecarrier; and a second opening formed in the material in fluidcommunication with the first opening.

In various embodiments, the second opening may extend through thematerial. In various embodiments, the device may further include amicrophone. In various embodiments, the microphone may include acorrugation. In various embodiments, the patterned mask may include anoxide. In various embodiments, the patterned mask may include silicondioxide.

In various embodiments, a method for manufacturing an opening structureis provided. The method may include: forming material over a first sideof a carrier covering at least a portion of the carrier; forming apatterned mask over the material; forming a second material over thematerial covering at least a portion of the material; forming a firstopening in the carrier from a second side of the carrier opposite thefirst side of the carrier to at least partially expose the material;forming a second opening in the material from the second side of thecarrier, thereby at least partially exposing the patterned mask; andforming a third opening in the second material using the patterned maskas a mask.

In various embodiments, a method for manufacturing an opening structureis provided. The method may include: forming a patterned mask in acarrier from a first side of a carrier; forming material over the firstside of the carrier covering at least a portion of the carrier; forminga first opening in the carrier from a second side of the carrieropposite the first side of the carrier to at least partially expose asurface of the patterned mask; and forming a second opening in thematerial from the second side of the carrier using the patterned mask asa mask.

In various embodiments, a device is provided. The device may include thefeatures of: a carrier comprising a first side and a second sideopposite the first side; a patterned mask formed in the carrier at thefirst side of the carrier; a first opening formed in the carrier,wherein the first opening extends between the first side of the carrierand the second side of the carrier, and wherein the first opening is atleast partially covered at a first end of the first opening by thepatterned mask; a material formed over the carrier on the first side ofthe carrier; and a second opening formed in the material in fluidcommunication with the first opening.

While the invention has been particularly shown and described withreference to specific embodiments, it should be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims. The scope of the invention is thusindicated by the appended claims, and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced.

What is claimed is:
 1. A device, comprising: a carrier comprising afirst side and a second side opposite the first side; a patterned maskformed over the first side of the carrier; a first opening extendingthrough the carrier from the first side of the carrier to the secondside of the carrier, wherein the first opening is at least partiallycovered at the first side of carrier by the patterned mask; a materialformed over the first side of the carrier; and a second opening formedin the material that is in fluid communication with the first opening.2. The device of claim 1, wherein the second opening extends through thematerial.
 3. The device of claim 1, wherein the patterned mask comprisesan oxide.
 4. The device of claim 3, wherein the patterned mask comprisessilicon dioxide.
 5. The device of claim 1, wherein the patterned maskcomprises carbon.
 6. The device of claim 1, wherein the patterned maskcomprises at least one opening through the patterned mask.
 7. The deviceof claim 1, wherein the material directly contacts the carrier at thefirst side.
 8. The device of claim 7, wherein the material covers andcontacts one or more outer sidewalls of the patterned mask.
 9. Thedevice of claim 1, wherein a lateral width of the first opening islarger than a lateral width of the second opening, the lateral widthsbeing measured along a direction parallel to the first side of thecarrier.
 10. The device of claim 1, further comprising: a front sidestructure over a first side of the material facing away from thecarrier.
 11. The device of claim 10, wherein a sidewall of the secondopening extends from the first side of the carrier to the front sidestructure.
 12. The device of claim 10, wherein the front side structurecomprises a microphone.
 13. The device of claim 12, wherein themicrophone comprises a corrugation.
 14. The device of claim 1, wherein avirtual plane, that coincides with a sidewall of the first opening andextends beyond the carrier towards the patterned mask, intersects thepatterned mask.
 15. The device of claim 1, wherein the first opening hasa lateral width of the opening that increases continuously from thesecond side of the carrier to the first side of the carrier, the lateralwidth being measured in a direction parallel to the first side of thecarrier.
 16. The device of claim 1, wherein the first opening is formedinto the carrier so that at least a portion of a first mask portion ofthe patterned mask facing the carrier and at least a portion of a secondmask portion of the patterned mask facing the carrier are exposed by thefirst opening through the carrier in a direction perpendicular to thefirst side of the carrier.
 17. The device of claim 1, furthercomprising: a third opening formed in first layer, wherein the first,second, and third openings are in fluid communication.
 18. A device,comprising: a carrier comprising a first side and a second side oppositethe first side; a patterned mask formed in the carrier at the first sideof the carrier; a first opening formed in the carrier, wherein the firstopening extends between the first side of the carrier and the secondside of the carrier, and wherein the first opening is at least partiallycovered at a first end of the first opening by the patterned mask; amaterial formed over the carrier on the first side of the carrier; and asecond opening formed in the material in fluid communication with thefirst opening.